The present invention relates to a burst output timing control system in a satellite communication system for performing radio communication between a central earth station and a plurality of remote earth stations via a satellite.
In a conventional satellite communication system, data communication is performed by a slotted ALOHA method using a star network. In this case, the distances from the areas in which remote earth stations are installed to a central earth station are different from each other. That is, the times taken for data from remote earth stations to reach the central earth station vary depending on the locations of the remote earth stations. For this reason, in the conventional system, burst data from each remote earth station is monitored in the central earth station, and the transmission timing of each burst data is adjusted in each remote earth station such that the time taken for each burst data to reach the central earth station becomes a predetermined time.
In such a conventional burst output timing control system, however, burst data from the respective remote earth stations must be monitored in the central earth station, and the monitor results must be informed to the respective remote earth stations to perform timing adjustment suitable for each remote earth station, resulting in cumbersome adjustment.
A transmission timing adjustment system is disclosed in Japanese Patent Laid-Open No. 3-128532. According to this system, in a time division multiple access radio communication system for performing radio communication between one central earth station and a plurality of remote earth stations by using burst signals, a timing adjustment signal is transmitted from each remote earth station to the central earth station within a control slot set in a corresponding transmission frame. In the central earth station, shifts in the reception phase of this timing adjustment signal from 0.degree. and 180.degree. as normal phases are detected, and a smaller value of the detected phase shifts is set as a detected phase shift amount. Information representing this phase shift amount is then informed to the remote earth station which has transmitted the above timing adjustment signal. The remote earth station adjusts its own transmission phase to nullify the phase shift amount in accordance with the information representing the phase shift amount and informed from the central earth station. Thereafter, a timing adjustment signal is transmitted from the remote earth station to the central earth station at the transmission timing set after the phase shift adjustment, and the central earth station detects the bit shift amount of the reception timing of this timing adjustment signal with respect to the normal reception timing in units of 1/2 bits. The central earth station informs the remote earth station, which has transmitted the above timing adjustment signal, of information representing this detected bit shift amount. The remote earth station adjusts its own transmission timing to nullify the bit shift amount in accordance with the information representing the bit shift amount.
If the output timing of burst data is adjusted by applying this transmission timing adjustment scheme to a satellite communication, the above problem of cumbersome adjustment can be solved.
In this output timing adjustment scheme, however, a control area is required in data because a timing adjustment signal is transmitted from a given remote earth station to the central earth station within a control slot set in a corresponding transmission frame. In addition, the central earth station requires a special circuit for detecting the timing adjustment signal. Therefore, a complicated hardware arrangement is required.